Conventionally, in the electrostatic recording process in copying machines, facsimiles, printers and the like, a printing method has been adopted in which the surface of a photosensitive drum is electrically charged uniformly, an image is projected from an optical system onto the surface of the photosensitive drum to eliminate the electric charges of the light-irradiated areas, thereby forming an electrostatic latent image, then a toner is supplied to the electrostatic latent image to electrostatically adhere the toner to the latent image, thereby forming a toner image, and the toner image is transferred onto a recording medium such as a paper, an OHP sheet, a printing paper, etc.
As a photosensitive drum for use in such an electrostatic recording process, conventionally, one which has the structure shown in FIG. 1 has been generally used.
Specifically, in the photosensitive drum generally used, flanges 2a, 2b are fittingly fixed to both ends of a cylindrical base 1 having good electrical conductivity, and a photosensitive layer 3 is formed on the outer peripheral surface of the cylindrical base 1. As shown in FIG. 1, ordinarily, the photosensitive drum is rotatably supported in the condition where support shafts 4, 4 provided in a main body a of the electrophotographic apparatus are inserted in shaft holes 5, 5 provided in both the flanges 2a, 2b, and a gear 7 connected to a drive source such as a motor is meshed with a drive gear 6 formed on the flange 2b on one side so that the photosensitive drum can be driven to rotate.
In this case, as a material for forming the cylindrical base 1, aluminum alloys have hitherto been used since they are comparatively light in weight, excellent in machinability, and good in electrical conductivity.
However, in the case of using the cylindrical base formed of an aluminum alloy, in order to meet the requirements for strict dimensional accuracy and for a predetermined surface roughness, high-precision machining must be conducted individually, and both ends of the cylindrical base must be machined for the fitting and fixation of the flanges 2a, 2b thereto. In some cases, further, a processing may be required for preventing the oxidation of the surface or the like. Therefore, in view of an increased number of manufacturing steps and a raised manufacturing cost, the aluminum alloys are not necessarily satisfactory for use as material for forming the cylindrical base constituting the photosensitive drum.
On the other hand, the formation of a resin-made cylindrical base 1 by use of a conductive resin composition containing a conductive agent such as carbon black mixed and dispersed in a resin base material has also been proposed. For example, Patent Document 1 (Japanese Patent Laid-open No. 2002-372794) discloses a method in which at least one selected from a polyamide resin and a polyester resin is used as a main constituent of a resin base material, and a low-water-absorptivity resin is blended in the resin base material to lower the water absorption of the conductive resin composition to 1.5% or below, whereby a photosensitive drum having a high dimensional stability even under high-temperature high-humidity use conditions can be obtained.
However, in forming a photosensitive layer on a cylindrical base formed of the conductive resin composition containing a polyester resin as a main constituent of the resin base material, the adhesion between the photosensitive layer and the cylindrical base may be insufficient in some cases. In such a case, the surface of the base may be roughened by an after-processing, but such an after-processing may lead to a rise in the manufacturing cost. In addition, since the polyester resin is a crystalline thermoplastic resin, the resin is high in shrinking property, so that there is still a room for improvement as to the dimensional accuracy of the formed product.
The present invention has been made in consideration of the above-mentioned circumstances. Accordingly, it is an object of the present invention to provide a base for a photosensitive drum which is excellent in chemical resistance, formability, dimensional accuracy and adhesion to a photosensitive layer and is excellent in dimensional stability, and a photosensitive drum using the base.